IEEE-802.11ax--High-Efficiency-WLANs

arXiv:1501.01496v4[cs.NI]28Jul2015IEEE802.11ax:High-EfficiencyWLANs∗BorisBellaltaUniversitatPompeuFabra,BarcelonaAbstractIEEE802.11ax-2019willreplacebothIEEE802.11n-2009andIEEE802.11ac-2013asthenexthigh-throughputWirelessLocalAreaNetwork(WLAN)amendment.Inthispaper,wereviewtheexpectedfutureWLANscenariosanduse-casesthatjustifythepushforanewPHY/MACIEEE802.11amendment.Afterthat,weoverviewasetofnewtechnicalfeaturesthatmaybeincludedintheIEEE802.11ax-2019amendmentanddescribeboththeiradvantagesanddrawbacks.Finally,wediscusssomeofthenetwork-levelfunctionalitiesthatarerequiredtofullyimprovetheuserexperienceinnext-generationWLANsandnotetheirrelationwithotheron-goingIEEE802.11amendments.Keywords:IEEE802.11ax,WLANs,High-efficiency,DenseNetworks1IntroductionIEEE802.11WirelessLocalAreaNetworks(WLANs)[1]areacost-efficientsolutionforwirelessInternetaccessthatcansatisfymostcurrentcommunicationrequirementsindomestic,publicandbusinessscenarios.Similartootherwirelesstechnologies,WLANshaveevolvedbyintegratingthelatesttechno-logicaladvancesinthefieldassoonastheyhavebecomesufficientlymature,aimingtocontinu-ouslyimprovingthespectrumutilizationandtherawWLANperformance.IEEE802.11n-2009adoptedSingle-userMultipleInputMultipleOutput(SU-MIMO),channelbondingandpacketaggregation.ThosemechanismswerefurtherextendedinIEEE802.11ac-2013,whichalsoin-troducedDownlinkMulti-user(MU)MIMOtransmissions.Inaddition,newamendmentssuchastheIEEE802.11af-2013andtheIEEE802.11ah-2016arefurtherexpandingtheapplicationscenariosofWLANs,whichincludecognitiveradio,long-rangecommunication,advancedpowersavingmechanisms,andsupportforMachinetoMachine(M2M)devices.Partlybecauseoftheirownsuccess,next-generationWLANsfacetwomainchallenges.First,theymustaddressdensescenarios,whichismotivatedbythecontinuousdeploymentofnewAccessPoints(APs)tocovernewareasandprovidehighertransmissionrates.Second,thecurrentevolutionofInternetusagetowardsreal-timehigh-definitionaudioandvideocontentwillalsosignificantlyincreaseusers’throughputneedsintheupcomingyears.∗AcceptedforpublicationinIEEEWirelessCommunicationsMagazine.July20151Toaddressthosechallenges,theHigh-EfficiencyWLAN(HEW)TaskGroup[2]iscurrentlyworkingonanewhigh-throughputamendmentnamedIEEE802.11ax-2019.Thisnewamend-mentwilldevelopnewphysical(PHY)andmediumaccesscontrol(MAC)layerenhancementstofurtherimprovetheWLANperformance,withafocusonthethroughputandbatteryduration.Thisarticleoverviewssomeofthosenewenhancementsanddescribesthepotentialbenefitsanddrawbacksofeachone.Wehavegroupedtheseenhancementsintofourmaincategories:spatialreuse,temporalefficiency,spectrumsharingandmultiple-antennatechnologies.Moreover,wealsodiscussseveralkeysystem-levelimprovementsfornext-generationWLANs,asinadditiontotheIEEE802.11ax-2019amendment,theywilllikelyimplementotherin-progressamend-mentssuchasIEEE802.11aq-2016(pre-associationdiscoveryofservices),IEEE802.11ak-2017(bridgednetworks)andIEEE802.11ai-2016(fastinitiallinksetuptime)tosatisfythecreatedexpectations.2Scenarios,Use-casesandRequirementsTheforecastnumberofdevicesandnetworks,thetrafficcharacteristicsanduserdemandsforthe2020-2030decademotivatethedevelopmentofanewPHY/MACIEEE802.11amendmenttocopewiththenewchallengesandusagesWLANswillface[2].OneofthemostrepresentativecharacteristicsofWLANsistheuseofCarrierSenseMultipleAccess(CSMA/CA)asMACprotocol.Itoffersareasonabletrade-offbetweenperformance,robustnessandimplementationcosts.UsingCSMA/CA,whenanodehasapacketreadyfortransmission,itlistenstothechannel.Oncethechannelhasbeendetectedfree(i.e.,theenergylevelonthechannelislowerthantheCCA(ClearChannelAssessment)threshold,thenodestartsthebackoffprocedurebyselectingarandominitialvalueforthebackoffcounter.Thenodethenstartsdecreasingthebackoffcounterwhilesensingthechannel.Wheneveratransmission,fromeitherothernodeswithinthesameWLANorthosebelongingtootherWLANs,isdetectedonthechannel,thebackoffcounterwillbepauseduntilthechannelisdetectedfreeagain,atwhichpointthecountdownisresumed.Whenthebackoffcounterreacheszero,thenodestartstransmitting.Figure1(a)showsanexampleoftheCSMA/CAoperation.2.1DenseWLANscenariosProvidinghighdataratesinscenarioswherethedensityofWLANusersisveryhigh(e.g.,1user/m2)requiresthedeploymentofmanyAPsplacedclosetoeachother(e.g.,within5-10mofoneanother).Figure1depictsanddescribesthreeofthosescenarios:a)astadiumb)atrain,andc)anapartmentbuilding.Inthesedensescenarios,mostrelevantchallengesarerelatedtointerferenceissues,whichincreasethepacketerrorrateandreducethenumberofconcurrenttransmissionsinagivenareabypreventingneighboringWLANsfromaccessingthechannel.Additionally,thepresenceofmanystations(STAs)inthesameareaincreasesthechancesthatthebackoffcountersoftwoormoreSTAsreachzerosimultaneously,whichresultsinacollision.Inthestadiumscenario,manypeopleareconcentratedinsmallareasbecauseofafair,a2tAPSTASTADATAACKsuccessfultransmissionbackoffcountdownbusychannelcollisionbetweentwotransmissions(a)ExampleofCSMA/CAtemporalevolutionwithoneAPandtwoSTAsScenario(Area,m2)APsSTAsDescriptionStadium(∼12500m2)100050000LargeeventsthatrequiremanyAPstoprovideasati